(1) Field of the Invention
The field of application to which the present invention pertains is liquid crystal display devices.
(2) Related Art Statement
As the speed of communication of portable information devices and the capacitance of memories increase, video information having greater capacitance and moving images having a greater number of frames can be handled. Display devices, which are the interface, are required more than ever to have higher image quality, larger screens and a greater number of pixels. Meanwhile, the designs have been reviewed as the portable information devices market has matured, and thin, stylish designs tend to be preferred. Together with this, thinner display devices are required.
IPS (in-plane switching) type liquid crystal display devices have an in-plane electric field of which the main component is parallel to the plane of the liquid crystal formed between pixel electrodes and common electrodes formed on the same substrate, and thus, the liquid crystal layer is driven. Therefore, in the IPS type liquid crystal display devices, rotation within the liquid crystal layer is a main change in the alignment of the liquid crystal layer as an electric field is applied. In the VA (vertically aligned) type, the ECB (electrically controlled birefringence) type, the OCB (optically compensated birefringence)-type and the like, a change in the alignment of the liquid crystal layer as an electric field is applied is mainly a change in the tilt angle, while the change in the tilt angle is small in the IPS type liquid crystal display devices. As a result, a change in the effective value of retardation is small as a voltage is applied in the IPS type liquid crystal display devices, and a display excellent in the gradation reproducibility can be gained in a wide view angle range. Therefore, the demand for an increase in the image quality can be more satisfied in the IPS type liquid crystal display devices.
In addition, in the VA type used as middle- and small-sized liquid crystal displays, the view angle properties increase through the conversion to multi-domains, and at this time, quarter wavelength plates are layered between the liquid crystal panel and the upper and lower polarizers in order to prevent the lowering of the transmittance. The quarter wavelength plates cause the thickness of the VA type liquid crystal display devices to increase. However, the IPS type liquid crystal display devices do not require a quarter wavelength plate, and therefore, the demand for a reduction in the thickness can be more satisfied.
Liquid crystal display devices, including the IPS type, are generally non-light emitting type display devices, and therefore, the brightness of the display is determined by the transmittance in addition to the brightness of the light source. There are examples focusing on the elastic constant of the liquid crystal layer in order to increase the transmittance of the IPS type liquid crystal display devices (for example, Patent Document 1).
[Patent Document 1] Japanese Unexamined Patent Publication 2002-296611